Extreme pressure lubricant



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acidic extreme pressure additives.

United States Patent 2,755,250 EXTREME PRESSURE LUBRICANT Forrest J.Watson, Berkeley, and Paul H. Williams,

Orinda, Califi, as'signors to Shell Development Company, New York, N.Y., a corporation of Delaware No Drawing. Application March 28, 1955,Serial No. 497,404

8 Claims. 01. 252-56) This invention relates to lubricants particularlysuitable for lubrication under extreme operating conditions, such asunder extreme pressure, high speed and high temperature conditions.

It is well known that the high pressures occurring in certain types ofgears and bearings may cause a film of lubricant to rupture with theconsequent damage to the machinery. It has been shown that baselubricants, such as mineral oil, can be improved with regard to theirprotective effect, particularly on rubbing surfaces by the addition ofcertain substances, so that excessive wear, scuffing and seizure (whichnormally follow a break in the film of lubricant) can be prevented evenunder the most unfavorable pressure and speed conditions. Lubricantspossessing this highly desirable property are called extreme pressurelubricants.

It is known that elements or certain compounds of elements of the typeof chlorine, sulfur, phosphorus and lead are capable of impartingextreme pressure properties to lubricants which may be lubricating oilsor greases. Among the compounds heretofore used are notably the leadsoaps, phosphoric acid esters, free or loosely bound sulfur, and certainchlorinated organic compounds. Two principal objections have beenencountered in the use of these and like materials. Firstly, they arehighly reactive with the contacting metal surfaces causing etching,corrosion and discoloration of said surfaces; because of this, theseadditives alter the original chemical nature of the contacting surfaceand result in the rapid depletion from the lubricant of the extremepressure additive. The second'objection or defect is of substantialimportance with respect to the maintenance of a uniform extreme pressurelubricating composition: This defect resides in the tendency of many ofthe materials known to be useful for their extreme pressure impartingfunction to separate from the lubricating medium. In overcoming thelatter disadvantage, it has been found that a limited amount of thematerial may be kept in colloidal suspension in a luene fluids as asolvent type base for certain water-soluble I In the latter system itwas found possible to dissolve amounts in the order of about 2% of theacidic substances in the base lubricant without the aid of the surfaceactive materials necessary when mineral oil is the base employed-However, even here there is a limiting concentration which will dissolvein the base fluid and consequently a limit placed upon the pressureswhich suchlubricants can stand before rupturing.

It is an object of the present invention to provide improved extremepressure lubricating compositions. It is a further object of the presentinvention to provide ho-' mogeneous extreme pressure lubricatingcompositions exhibiting outstanding extreme pressure properties. Otherobjects will become apparent during the following discussion.

Now, in accordance with the present invention, it has been found thatsubstantially greater proportions of extreme pressure agents can be usedand much greater effectiveness of the extreme pressure limitations canbe obtained by forming homogeneous solutions in water-misciblepolyoxyalkylene fluids of the heat condensation products formed betweenwater-soluble aliphatic hydroxy carboxylic acids and the lower aliphaticpolyhydric alcohols.

The subject compositions referred to above have been found to possessthe advantageous property of complete miscibility even in the absence ofdispersing agents and when the composition is anhydrous or contains onlysmall amounts of water (e. g. less than 5% by Weight of thepolyoxyalkylene fluid) in higher concentrations than can be obtained bythe use of the acids per se in the same fluid. It is preferred that thepresence of water be held at a maximum not exceeding 2% by Weight ifpossible and in most cases the presence of water is found to be entirelyunnecessary in order tov form homogeneous solutions between the heatcondensation products and the water-soluble polyoxyalkylene fluids. Bywater-soluble acids is meant those acids of the recited class having asolubility of at least 0.5% by weight in Water at 20 C. Preferably thesolution is in the order of about at least 2% by weight in water.

The water-miscible polyoxyalkylene fluids are distinguished from thecorresponding classes ofpolyoxyalkylene fluids which are miscible inaliphatic hydrocarbons including mineral oils. Water miscibility istaken to mean the formation of clear uniphase mutual solutions when thefluid and water are mixed at room temperature (20 C.) in anyproportions. The classes of materials with which this invention isconcerned are those having an average molecular Weight of at least abou250 and usually below about 1500. Polyoxyalkylene fluids of lowermolecular weight such as the tripropylene glycol monoethers, aresuitable solvents for the subject classes of additives but do notexhibit proper lubricating characteristics or extreme pressureproperties. For the most part the polyoxyalkylene fluids which aremiscible with Water comprise mixtures of polymers of lower molecularweight epoxides and glycols. Polyethylene glycols having averagemolecular weights between about 250 and 750 are suitable. Monoestersofsaid glycols with fatty acids having less than about eight carbon atomsper molecule and monoethers of alcohol having less than about ten carbonatoms also may be utilized.

The preferred classes of water-miscible fluids for use in the presentcompositions comprise the copolymers of ethylene oxide and 1,2-propyleneoxide, as well as the monoethers thereof, particularly when the oxideratio is 25 to 10-90 ethylene oxide-1,2-propylene oxide. By the ratiofrom 7525 to 10-90 is meant that, in the oxide mixture which may be usedin forming the copolymers the amount of 1,2-propylene oxide in themixture is from /3 to 9 times the amount of ethylene oxide present, byweight, the parts or proportion of the 1,2-propylene oxide being givenlast. These materials are described in two United States patents,namely, U. S. 2,425,755 to Roberts et a1. and U. S. 2,425,845 toToussaint et al. The

materials preferred for use in the subject compositions are those havingmolecular weights of at least about 250 and preferably below about 1500.The unmodified diols falling within these limitations may be employed orthe monoethers thereof may be used. In the preparation of themonoethers, alcohol having from 1 to about carbon atoms are preferred,and still more preferably these are aliphatic monohydric alcohols havingthe above carbon chain.

The subject polyoxyalkylene fluids may be prepared by polymerization oflow molecular weight alkylene glycols to form a closely similar class ofpolymers. The epoxides and glycols are preferably those having from 1 to4 carbon atoms each and it is further preferred that the epoxide linkageor the glycol radicals be attached to adjacent carbon atoms. Suitableglycols for use in the formation of water-miscible polymers includeethylene glycol, 1,2- propylene glycol, trimethylene glycol and butyleneglycol.

The heat condensation products to be employed as dissolved additives inthe above class of water-soluble polyoxyalkylene fluids comprise thoseformed between water-soluble aliphatic hydroxy carboxylic acids andlower aliphatic polyhydric alcohols. The term heat condensation productappears to be the best way of describing the products to be used, sincethe products are somewhat indeterminate in composition. The followingacids comprise those most preferred in the preparation of the subjectheat condensation products:

Hydroxy acids:

Monohydroxy fatty acids:

Glycollic acid Lactic acid l-ethylidene lactic acid 2-ethylidene lacticacid Ethylene lactic acid Hydroxy caproic acid a-Hydroxy butyric acidAcetonic acid Leucic acid e-Hydroxy crotonic acid u-Hydroxy valeric acidPolyhydroxy fatty acids:

Glyceric acid Arabonic acid Gluconic acid Gulonic acid Galactonic acidTalonic acid Mannonic acid Hydroxy polycarboxylic acids:

Citric acid Tartaric acid Trihydroxyglutaric acid Saccharic acidTartronic acid Malic acid The polyhydric alcohols which may be employedin the preparation of the subject heat condensation products arepreferably the lower alkylene glycols containing from 2 to 6 carbonatoms per molecule, such as ethylene glycol, diethylene glycol,triethylene glycol, propylene glycol, dipropylene glycol, butyleneglycol, and the like. While these glycols are preferred, carbohydratesmay be employed, such as sugars and derivatives thereof. The pentosesand hexoses are favored including ribose, arabinose, glucose, fructose,galactose and mannose, as well as hexitols, such as sorbitol ormannitol. The mixtures to be heat treated should predominate on a weightbasis with respect to the hydroxy carboxylic acids and it is preferredthat the mixture to be treated contain from 75 to 90% by Weight based onthe mixture of the subject class of acids.

In carrying out the heat condensation, the physical mixture is simplyheated to a temperature between about 100 and 200 C. for a periodvarying from about onehalf to about 4 hours. Under these conditions, ithas been found that a complex series of reactions occur, the

two predominating comprising polymerization of the acids andsimultaneous esterification of the acids or of the polymerizationproducts thereof. The course of the condensation can be followed bymeasuring the quantity of Water evolved during the condensation process,since both the polymerization and esterification reactions result in theformation of water. It is preferred that the proportion of water formedduring the process be between about 5 and about 12% by weight of theoriginal mixture. Under these conditions, the product has been found tobe most readily soluble in the subject class of water-misciblepolyoxyalkylene fluids. Still more preferably, the proportion of waterevolved during the heat condensation period is between about 6.5 and9.5% by weight of the original mixture. It is a preferred practice toremove this water as it is formed but limited amounts may be permittedto remain in the product to assist in dissolving the latter in thewater-miscible polyoxyalkylene fluids.

The act of solution of the heat condensation product is to be carriedout subsequent to heat condensation and normally will comprise simplestirring, possibly aided by mild heating or warming to hasten thedissolving. Preferably the period of heating is between aboutthreequarters and 1% hours at temperatures between about 50 C. and aboutC.

In accordance with one phase of the present invention, it has beendiscovered that the subject heat condensation products will dissolve inthe above described watermiscible polyoxyalkylene fluids to a muchlarger extent than the corresponding acids themselves. While acids suchas tartaric acid are soluble in the subject class of fluids to theextent of about 2% by weight, it has been ascertained that the subjectheat condensation products formed for example between tartaric acid andpropylene glycol will dissolve in amounts up to about 10-12% by weightof the polyoxyalkylcne fluid, dependent upon the proportion of acid toglycol and upon the extent to which the complex condensation heattreatment has been carried out.

In further accordance with the present invention, it has beenascertained that not only is it possible to incorporate far greaterproportions of the heat condensation products in the subject class offluids than is pos sible with the acids themselves, but also theresulting compositions have wider applicability than do the same fluidscontaining only the unmodified acids. More specifically, it has beenfound by extensive testing that water-soluble polyoxyalkylene fluidsmodified by the presence of acids such as tartaric acid and other acidsas listed hereinbefore are not satisfactory for the op eration of gearswherein intensive high pressures and rubbing action occur, as in hypoidgears. Under these conditions, the last described compositions causeseizure after onlya short period of operation. As opposed to this, thecompositions of the present invention have been found to provideextremely satisfactory operation in bypoid gears as further described inthe working examples appearing hereinafter. The following examplesillustrate the present invention:

Example 1 Fifteen parts by weight of propylene glycol and 85 parts byweight of tartaric acid are heated for one hour from room temperature toabout C. and thereafter for another hour at about 150 C. During thistime water was lost due to polymerization of the acid and/oresterification of the acid by the glycol. 6.8% by weight of water waslost during this period. The product was a viscous resin which uponcooling became solid.

Another condensation product can be prepared by heating the sameproportion of the same reactants for about one-half hour to atemperature of 150 C. and thereafter for an hour at a temperaturebetween 150 and C. to cause a water loss of 9.2% based on the originalingredients of the mixture. This product had a w st higher molecularweight than that described above and did not dissolve as readily in thesubject polyoxyalkylene water-soluble fluids. v

A third product was prepared by heating the same proportions ofreactants and the same reactants for a period of about one hour to atemperature of 150 C. and thereafter for about one-half hour to atemperature of 162 C. This caused a water formation of 7.3% which waseliminated from the reaction mixture.

Four per cent by weight of the reaction product can be dissolved in ahigh viscosity polyoxyalkylene oxy-1,2- propylene glycol trade namedUcon 50 HB 660. When tested in a four-ball test machine at 1800 R. P. M.for a period of ten seconds under various loadings, it was found thatthe composition had an initial seizure load of 178 kg. anda Weld load of200 kg. The unmodified polyoxyalkylene fluid had an initial seizure loadof about 79 kg. and a weld load of about 141 kg.

Example 2 Eighty-five parts by weight of tartaric acid and 15 parts byweight of propylene glycol were heated together at a temperature betweenabout 160 and 170 C. for a period of 75 minutes. This caused a waterloss of about 6.5% from the reaction product. One hundred sixty grams ofthe product can be dissolved in 1440 grams of the polyoxyalkylene fluididentified in the previous ex ample. The product obtained when tested inthe fourball test machine had an initial seizure load (10 seconds) of224-251 kg. and a weld load of 251 kg.

This composition, when used for the lubrication of hypoid gears at apinion speed of about 2250 R. P. M. forward and 4000 rev. permittedrunning in either forward or reverse direction at the maximum load(about 100 p. s. i. forward, 50 p. s. i. rev.). The same fluid, omittingthe condensation product, caused scoring at low loads in the order ofabout p. s. i.

Example 3 Example 4 By heating about by weight of ethylene glycol and90% by weight of lactic acid for a period of about one hour at atemperature of 110 C., a product is obtained having a water loss ofabout 29%. The heat condensation product, which is a syrupy resin, whendissolved in a low viscosity polyoxyethylene oxy-1,2-propylene glycolfluid having water-soluble properties to the extent of 10% by weightforms a lubricating composition having a four-ball initial seizure loadof 178 kg.

We claim as our invention:

1. A lubricant composition comprising a major amount of a water-misciblemixture of heteric oxyethylene oxy- 1,2-propylene diols in which theethylene oxide and 1,2- propylene oxide are combined therein asoxyethylene and oxy 1,2-propylene groups in a ratio which is at leastonethird part of 1,2-propylene oxide for each part of ethylene oxide byWeight, said diols containing in a single molecule both oxyethylene andoxy 1,2-p1'opylene groups, said mixture having an average molecularweight of at least 300 attributable to said groups, and a minor amountsufficient to improve the extreme pressure properties thereof of a heatcondensation product of a mixture of tartaric acid and propylene glycol,said mixture prior to condensation comprising a predominating proportionby Weight of tartaric acid said heat condensation being carried outbyheating the acid and glycol at a temperature between about 125 and 175C. for a period between about 0.5 and about 4 hours until between about6.5 and about 9.5% by weight of water, based on the mixture, is formed.

2. A composition according to claim 1 wherein the mixture of tartaricacid and propylene glycol prior to heat condensation thereof, comprisesbetween about and about by weight of tartaric acid.

3. A lubricant composition comprising a major amount of a water-misciblemixture of heteric oxyethylene oxy- 1,2propylene diols in which theethylene oxide and 1,2- propylene oxide are combined therein asoxyethylene and oxy 1,2-pr0pylene groups in a ratio which is at leastonethird part of 1,2-propylene oxide for each part of ethylene oxide byweight, said diols containing in a single molecule both oxyethylene andoxy 1,2-propylene groups, said mixture having an average molecularweight of at least 300 attributable to said groups, and a minor amountsufficient to improve the extreme pressure properties thereof of a heatcondensation product of a mixture of a watersoluble monohydroxy fattyacid having 2-6 carbon atoms per molecule and a lower alkylene glycolhaving between 2 and 6 carbon atoms per molecule formed by heating for aperiod between about 0.5 and about 4 hours at a temperature betweenabout and 200 C. until between about 5 and about 12% by weight of Water,based on the mixture, is formed.

4. A composition according to claim 3 containing in addition betweenabout 0.5% and about 5% by weight of water.

5. A lubricant composition comprising a major amount of a water-misciblemixture of heteric oxyethylene oxy 1,2-propylene diols in which theethylene oxide and 1,2- propylene oxide are combined therein asoxyethylene and oxy 1,2-pr0pylene groups in a ratio which is at leastonethird part of 1,2-propylene oxide for each part of ethylene oxide byweight, said diols containing in a single molecule both oxyethylene andoxy 1,2-propylene groups, said mixture having an average molecularweight of at least 300 attributable to said groups, and a minor amountsufficient to improve the extreme pressure properties thereof of a heatcondensation product of a mixture of a watersoluble aliphatic carboxylicacid containing 3-6 carbon atoms per molecule and having at least onehydroxy substituent and propylene glycol formed by heating for a periodbetween about 0.5 and about 4 hours at a temperature between about 100and about 200 C. until between about 5 and about 12% by weight of water,based on the mixture, is formed.

6. A lubricating composition adapted for extreme pressure use comprisinga major amount of a water-miscible mixture of monohydroxy oxyethyleneoxy 1,2-propylene aliphatic monoethers in which the ethylene oxide and1,2- propylene oxide are combined therein as oxyethylene and oxy1,2-propylene groups in a ratio which is at least onethird part of1,2-propylene oxide for each part of ethylene oxide by weight, saidmixture having an average molecular weight of at least 300 attributableto said groups, the aliphatic monoethers of said mixture containing in asingle molecule both the oxyethylene and oxy 1,2-propylene groups and aminor amount sufiicient to improve the extreme pressure propertiesthereof of a heat condensation product of a mixture of an aliphatichydroxy polycarboxylic acid having 2-3 carboxyl radicals, 1-2 hydroxylgroups, and a total of 3-6 carbon atoms per molecule and a loweralkylene glycol having between 2 and 6 carbon atoms per molecule formedby heating for a period between about 0.5 and about 4 hours at atemperature between about 100 and 200 C. until between about 5 and about12% by weight of water, based on the mixture, is formed.

7. A lubricating composition comprising a major amount of awater-miscible polyoxyalkylene fluid and a minor amount suflicient toimprove the extreme pressure properties thereof of a mixture of a heatcondensation product or a mixture of a water-soluble aliphaticcarboxylic acid containing 36 carbon atoms per molecule and having atleast one hydroxy substituent and a lower aliphatic glycol havingbetween 2 and 6 carbon atoms per molecule forrned by heating for aperiod between about 0.5 and about 4 hours at a temperature betweenabout 100 and about 200 C. until between about 5 and about 12% by weightof water, based on the mixture, is formed.

8. A lubricant composition comprising a major amount of a water-misciblemixture of heteric oxyethylene oxy 1,2 '-propylene diol's in which theethylene oxide and 1,2- propylerie oxide are combined therein asoxyethylene and oxy 1,2-prop'ylene groups in a ratio which is at leastonethird part of 1,2-propy1ene oxide for each part of ethylene oxide byweight, said diols containing in a single molecule both oxyethylene andoxy 1,2-propylene groups, said mixture having an average molecularweight of at least 300 attributable to said groups, and a minor amountsufficient to improve the extreme pressure properties thereof of a heatcondensation product of a mixture of tartaric acid and propylene glycolformed by heating for a period between about 0.5 and about 4 hours at atemperature between about C. and about C. until between about 6.5 andabout 9.5% by weight of water, based on the mixture, is formed.

References Cited in the file of this patent UNITED STATES PATENTS2,147,647 Gleason Feb. 21, 1939 2,152,683 Eichwald Apr. 4, 19392,370,300 Farrington Feb. 27, 1945 2,430,842 Young Nov. 11, 1947 OTHERREFERENCES Ucon"-Fluids and Lubricants-Carbide and Carbon Chem. Corp.,New York, May 31, 1948; page 3 pertinent.

3. A LUBRICANT COMPOSITION COMPRISING A MAJOR AMOUNT OF A WATER-MISCIBLEMIXTURE OF HETERIC OXYETHYLENE OXY1.2-PROPYLENE DIOLS IN WHICH THEETHYLENE OXIDE AND 1,2PROPYLENE OXIDE ARE COMBINED THEREIN ASOXYETHYLENE AND OXY 1,2-PROPYLENE GROUPS IN A RATIO WHICH IS AT LEASTONETHIRD PART OF 1,2-PROPYLENE OXIDE FOR EACH PART OF ETHYLENE OXIDE BYWEIGHT, SAID DIOLS CONTAINING IN A SINGLE MOLECULE BOTH OXYETHYLENE ANDOXY 1,2-PROPYLENE GROUPS, SAID MIXTURE HAVING AN AVERAGE MOLECULARWEIGHT OF AT LEAST 300 ATTRIBUTABLE TO SAID GROUPS, AND A MINOR AMOUNTSUFFICIENT TO IMPROVE THE EXTREME PRESSURE PROPERTIES THEREOF OF A HEATCONDENSATION PRODUCT OF A MIXTURE OF A WATERSOLUBLE MONOHYDROXY FATTYACID HAVING 2-6 CARBON ATOMS PER MOLECULAR AND A LOWER ALKYLENE GLYCOLHAVING BETWEEN 2 AND 6 CARBON ATOMS PER MOLECULE FORMED BY HEATING FOR APERIOID BETWEEN ABOUT 0.5 AND ABOUT 4 HOURS AT A TEMPERATURE BETWEENABOUT 100 AND 200* C. UNTIL BETWEEN ABOUT 5 AND ABOUT 12% BY WEIGHTWATER, BASED ON THE MIXTURE, IS FORMED.